Our long-term objective is to elucidate the endocytic trafficking pathway of CFTR and to identify a drug that corrects defective endocytic trafficking of detaF508-CFTR. DeltaF508, the most common mutation in CF, reduces the expression of CFTR in the apical plasma membrane in epithelial cells because deltaF508-CFTR is not exported efficiently from the endoplasmic reticulum and because the endocytic trafficking of CFTR is abnormal. However, very little is known about the mechanisms regulating the endocytic trafficking of CFTR. In preliminary studies we demonstrate that myosin VI regulates CFTR endocytosis, that myosin Vc regulates CFTR endocytic recycling and that the deltaF508 mutation facilitates CFTR endocytosis. Accordingly, the hypothesis to be tested in this proposal is that a complex of interacting proteins including myosin VI and Vc regulates the endocytic trafficking of CFTR and that the deltaF508 mutation perturbs the endocytic trafficking pathway. To test this hypothesis we propose three specific aims: Specific Aim #1. Test the hypothesis that a macromolecular complex of proteins including myosin Vl, Dab2, AP-2 and clathrin regulate the endocytosis of CFTR. The goal of this specific aim is to elucidate how myosin Vl, the adaptor proteins Dab2 and AP-2, and clathrin regulate the endocytosis of CFTR, Specific Aim #2. Test the hypothesis that a macromolecular complex of proteins including myosin Vc and EBP50 regulate the endocytic recycling of CFTR. The goal of this specific aim is to elucidate how myosin Vc and EBP50 regulate the endocytic recycling of CFTR, and Specific Aim #3. Test the hypothesis that the half-life of deltaF508-CFTR in the plasma membrane is reduced due to an increase in endocytosis and/or a reduction in endocytic recycling. The goal of this specific aim is to determine if the deltaF508 mutation perturbs CFTR endocytosis and/or endocytic recycling. We anticipate that our studies will provide new insight into the mechanisms involved in cargo selection and vesicle trafficking as well as the etiology of several other "trafficking" disorders such as autosomal dominant distal renal tubular acidosis, Huntington's disease, Tangier's disease, Niemann-Pick disease type C, and polycystic kidney disease.